The present invention relates to agricultural machines such as a mower of the type comprising at least one rotary mower unit depending from a main mounting beam. More particularly, the invention relates to suspension and flotation means for agricultural machines which may be of the tractor mounted or pull type.
2. Description of the Prior Art
In known mowers of the type referred to above, normally there are provided two or more such rotary mower units and these may comprise an upright drum with a flange at the lower end thereof for supporting outwardly projecting impact cutter blades. All the mower units depend from a main beam in side-by-side relation, when in the operative position. Either a stationary, or a freely rotatable, ground-engaging, generally saucer-like support member or skid is provided underneath each rotary mower unit in a manner to support the mower on the ground during operation and to shield the cutter blade mounting means on the drum flanges. The main beam with the mower units depending therefrom is coupled to a three point hitch structure for attachment to a tractor in a manner so that the main beam may pivot in a fore-and-aft direction as well as float in an up-and-down direction relative thereto. The pivotal movement in a fore-and-aft direction is required so as to be able to move the mower from a transport position generally longitudinally and rearwardly of the tractor to an operative position generally transverse and offset relative to the tractor. The floatation in an up-and-down direction is required to allow the mower to follow the ground contour in operation.
Suspension and flotation means are provided between the three point hitch and the main beam to compensate a certain proportion of the weight of the mower so that the latter rests on the ground surface with only a limited ground pressure. With a reduced ground pressure, the ground-engaging supports are less subject to wear. Also the suspension and flotation means should assist the mower in floating over ground irregularities, thus avoiding damage to the turf, as well as the machine, whilst maintaining a substantially constant stubble length.
Many types of suspension and flotation means have already been designed for drum mowers and other tractor-mounted agricultural machinery. However, many of them are not entirely satisfactory. Some do not compensate sufficiently the weight of the mowers so that the ground pressure of the supporting members is too high, with the result that the mower and supporting members are dragged over the ground imparting undue stresses to the machine, the supporting members or skids wear fast, and the machine "bulldozes" or digs into the ground surface. The latter results in the turf being damaged and the cut hay to be mixed with soil. Regrowth of damaged turf is of course slowed down substantially. Furthermore the mower does not float smoothly over ground irregularities.
In the case of a twin-drum mower, it is not possible properly to adjust the ground pressure exerted by both mower units which means that in most cases the ground pressure of one mower unit exceeds the ground pressure of the other mower unit which is very undesirable. In other structures, it may be that the ground pressure can be adjusted in an acceptable manner but often the system is then not flexible enough to keep the mower in constant contact with the ground surface. Thus, when an obstruction or a depression in the ground is met, the mower lifts off the ground and tends to "jump" over the obstruction or depression which results in unequal and unacceptable stubble lengths.
In still a further arrangement, the ground pressure in normal conditions can be adjusted in an acceptable manner but as soon as a rise in the ground surface is met, the ground pressure is increased substantially and to an unacceptable degree. In other words, the system also is not flexible enough to "float" over ground irregularities. In such circumstances, a major portion of the weight of the mower structure and of the main beam is supported on the ground surface via the mower unit encountering the rise in the ground. This is disadvantageous as again it results in faster wear of the supporting skids and imparts high stresses to the mower units and the mower suspension on the three point linkage.
The foregoing disadvantages of known mowers become more critical when the forward speed of the tractor and the machine is increased and there is a growing tendency to increase the normal working speed of rotary mowers as much as possible in the interest of productivity. The disadvantages mentioned are equally more critical when the total machine weight is higher which is especially the case when a crop conditioner is attached to the mower structure to provide a mower-conditioner.
Another problem which may occur is the tilting of the mower around the left-hand side of the left-hand supporting member or skid during fast turns to the right. This problem occurs especially on machines with fixed supporting skids or members and with a pivotal mounting of the main beam to the three point hitch structure or to an intermediate beam around a fore-and-aft pivot axis, the pivot axis being positioned at a substantial height above the ground surface. However, the same tipping tendency may be experienced also with mower structures not having the above described fore-and-aft pivot axis. To understand this phenomenon, it is necessary to realise that in the operative position the mower is positioned rearwardly of the rear tractor wheels and to the right of the tractor. Therefore, when turning to the right, the mower is subjected to a pulling force from the tractor which is directed to the left, tending to cause the mower to slide to some extent to the left over the ground. This pulling force is exerted at a distance above the ground level, and when there is a fore-and-aft pivot axis between the mower structure on the one hand and the three point hitch structure or intermediate beam on the other hand, this pulling force will act on the pivot. This pulling force tends to tilt the mower structure about the left-hand side of the left-hand supporting member or skid, especially when the skid is mounted stationary and thus cannot allow the mower to "roll" over the ground surface. This lifting tendency increases as the turning speed of the tractor increases; as the distance between the mower and the rear tractor wheels increases, as the height of the point of application of the pulling force above the ground level increases and as the distance between the centre of gravity of the mower and said point of application decreases. Obviously, the above described unstability of a tractor mounted-mower is a severe drawback.
It is the object of the present invention to overcome or to attenuate one or more of the foregoing disadvantages of agricultural machinery such as mowers and mower-conditioners, for example.